This invention relates in general to dot matrix printers, and more specifically to a print head for a dot matrix printer which prints dots by propelling droplets of electrically conductive ink onto a record.
Dot matrix printers generally have been known and used for many years. In one common form of dot matrix printer, a plurality of elongated print rods or wires are mounted on a print head carriage with their ends vertically aligned and juxtaposed to a record to be printed. To print a given character, the print rods are selectively driven against the record at a plurality of column positions, collectively forming a single character. In other known arrangements, two-dimensional or horizontal arrays of print rods may be provided. Similar thermal printing heads have also been employed.
A particularly limiting problem of known dot matrix printers, both in terms of speed and mechanical life, is the requisite mechanical movement associated with impact printing of the dots onto a record. Obviously, a print head may be reciprocated rapidly across a printed record when it is not printing. But practical printing speeds are considerably slower because the print rods must be repetitiously driven at and retracted from the printed record several times for each printed character. Although frictional losses associated with such movement may be minimized through improved lubricants and low friction mounting means, the inertia of the moving print rods and the moving parts of the driving electromagnets nevertheless remains a limiting factor in connection with print speed.
Related problems to the mechanical movement of the printing elements are the problems of wear and vibration. Although, as stated above, friction and the resultant wear of the moving parts may be minimized, it nevertheless remains a limiting factor. Furthermore, the necessity for precision machining of the moving parts results in increased expense to the dot matrix print head. Similarly, vibration may be alleviated by structurally reinforcing the print head and its support members, but this also adds to the expense of the resultant printer. Thus, an attendant disadvantage of dot matrix printers which have been devised heretofore to eliminate or minimize the above problems is the expense of both the materials and manufacture of the intricate mechanical assemblies comprising the print heads of such printers.
Furthermore, the operation of a typical dot matrix printer is attended by a constant chattering, producing considerable noise. Thus, any reduction in the movement of mechanical parts in the print head affords a bonus in terms of environmental noise. The noise factor is substantially reduced by use of a thermal print head, but at the cost of a requirement for use of expensive thermally responsive recording paper.